In the prior art a plurality of floor coverings are known such as real wood veneer laminate floors. Due to the relative cost efficient production possibilities in particular indoor laminate floors have become more popular in the last decades. Such laminate floors allow for example to imitate in a simple and cost efficient way the optically pleasing appearance of different kinds of wood or other natural materials.
Laminate floors are composed of laminate panels that therefore are provided at their edges with groove and tongue connections for connecting the panels with each other. Typically, such laminate panels are composed of a central carrier layer made of wood or a wood-based material such as MDF, HDF, particle board or OSB and further thinner layers that fulfil different functions.
For example, the appearance that is visible to the user is produced with the aid of a décor layer on the top surface of the carrier layer. This décor layer is directly printed on the carrier layer by means of the so called direct printing process. However, most common is the use of décor papers. The term “laminate panel” shall herein include both panels with paper layers and also direct printed panels, which are not necessarily provided with paper layers, but with a resin layer on the top surface.
When producing the décor by way of a décor paper at first a proper paper layer is printed with a décor for example a real wood imitation or also with a stone imitation. The printed paper is then saturated with a proper resin typically with an amino resin such as melamine and/or urea-formaldehyde resin. The so impregnated paper is then typically cured before further use, so that it can be rolled up on rolls or can be deposited in sheets on pallets and can be stored.
For further usage the impregnated and cured décor paper layer is applied onto the carrier layer before the resin is cured in a further step. The final curing of the resin namely the final curing of the resin molecule chains (and not the curing of the aqueous resin mixture where merely water is extracted) can occur in a separate curing step for example by using radiation such as electron, ultra-violet or infrared radiation. Typically, the curing is however made by the influence of heat and pressure when pressing the layer systems.
Further paper or resin layers can be arranged above the décor layer such as so called overlays. Such overlays are produced similarly to the décor paper layer by means of impregnated papers. A thin suitable paper is impregnated with a resin such as amino resin and is applied onto the décor layer. When curing the overlay layer this firstly opaque paper layer becomes transparent such that the décor lying thereunder becomes visible. The overlay layer serves for protecting the décor against exterior influences and it is known to add abrasion-resistant particles such as corundum particles additionally to the resin that is used for impregnating the overlays in order to increase the abrasion resistance of the subsequent laminate panels. Additionally, a core paper and overlay can be provided with a surface structure when pressing and curing that may match the visible structure of the décor, and simulates for example the haptic impression of the wood surface.
A known difficulty with producing laminate panels in particular using amino resins is that at the latest when pressing various layers of the layer systems to be pressed retract differently. When curing the resins, with which for example décor and overlay paper layers are impregnated, a contraction occurs as a result of a chemical polycondensation. During pressing a plurality of chemical bonds are formed dissociating water. The water moves out of the cured amino resin layer when pressing and thereby the volume shrinks significantly. Also, the used papers can exert tractive forces on the carrier layer during pressing. By these contractions of the layers forces are created that can result in undesired deformations of the carrier layer. The carrier layer bends by the contraction concavely to the top in the direction of the décor layer, or overlay layer respectively, such that the formed panel can only be used with difficulty.
To avoid such deformation of the panels a so-called counteractor is applied to the back surface opposite to the décor in the prior art, which counteractor shall compensate for the traction effects on the top surface. The easiest possibility to provide a counteractor that has the same tractive effect as the layers on the top surface is applying the same layers as on the top surface of the panel also on the back surface, such that the contraction effects of these layers exactly cancel each other out. For cost reasons it is however often not desired to use the high value layers that are used for forming the visible top surface of the panel also on the back surface that it is not visible during use. For this reason combinations of simple cost-efficient counteracting paper and of cost-efficient resins have been developed that are used as a counteracting layer on the back surface of the laminate panels in order to reduce the undesired curvature of the panels during pressing.
A typical example from the prior art is described in DE 199 03 912 A1. According to the method described therein firstly a coloring layer is applied directly onto the top surface of the carrier layer for a laminate panel in the direct pressing process. Onto this décor layer an impregnated overlay paper and onto the back surface of the carrier layer a counteractor is applied in the form of an impregnated counteracting paper. Optionally, it is proposed in DE 199 03 912 A1 for example to dry the impregnated overlay paper and to apply onto it an additionally melamine resin layer into which corundum is sprinkled, in order to provide an abrasion resistant surface for the panel this way. After applying these layers they are pressed in order to produce the finished laminate.
A further example from the prior art is described in DE 10 2008 027 235 A1. According to the application a décor paper that is imprinted and impregnated with an amino resin is applied onto a carrier layer for a laminate panel. To reduce rejects that result from mispressings this patent application proposes to provide also on the back surface of the laminate panel a further décor in the form of an impregnated décor paper instead of a cost-efficient counteractor in the form of a simple counteracting paper and corresponding resin. In other words, in this patent application it is proposed to produce a laminate panel, both surfaces of which are décor surfaces. According to this application it is thereby possible, if during pressing one of the two décor surfaces is damaged, to use the panel nevertheless, because a substitute décor exists on the opposite surface.
Because for each single paper layer costly impregnation steps are necessary, it is desirable to reduce the number of (impregnated) paper layers. Accordingly, the German application DE 10 2007 062 941 A1 proposes a laminate panel with a counteractor that enables to spare the usage of a counteracting paper layer. Instead of using an impregnated counteracting paper it is proposed in this application to apply multiple thin layers of an amino resin directly onto a back surface of a carrier layer for a laminate panel, wherein respectively prior to the application of a further amino resin layer, the prior amino resin layer is pre-dried. Although, it is possible with this method to spare a counteracting paper the alternating application and drying of single thin resin layers is time, cost and process consuming.
With regard to the above cited prior art, the present invention has the problem to provide a laminate panel and a method for its production as well as a counteracting material, whereby it will become possible to spare a counteracting paper for the laminate panel in a more cost-efficient and simple way.
These and other problems that are mentioned when reading the following description or can be recognized by the person skilled in the art are solved with a laminate panel according to claim 1, a method for its production according to claim 16 and a counteracting material according to claim 23.